Abstract

A major thrust of photorefractive materials research has been to increase the coupling constant Γ and speed up response time. Previous two-beam coupling experiments using SBN:60 have shown that the space charge field E_sc, and therefore the coupling constant, can be increased to some degree by optimizing the characteristic fields E_n and Ed.¹,² However, since E_sc tends toward the smaller of E_N and E_d for no external field, any attempt to incrase E_sc by increasing E_n will have minimal effect since E_sc will be limited by the diffusion field E_d. By applying an external dc electric field E₀, the photoexcited carriers will tend to be driven into the traps half a grating period away, and E_sc will be limited by E_n = eN_A/ϵK for large E₀. Experimentally, Γ has been found to increase by almost a factor of 3 to over 10 cm⁻¹ in Cr-doped SBN:60 with an applied field of 10 kV/cm. In addition, for Rh-doped SBN:60, the response time has been found to get significantly faster with an applied field, decreasing by more than an order of magnitude from ~2 s for E₀ = 0 to 0.1 s with E₀ = 10. These results suggest potential applications in field-enhanced optical limiting, switching, and thresholding.

© 1989 Optical Society of America